Selective Lithiation, Magnesiation, and Zincation of Unsymmetrical Azobenzenes Using Continuous Flow

A mild and general set of metalation procedures for the functionalization of unsymmetrical azobenzenes using a commercially available continuous-flow setup is reported. The metalations proceed with TMPLi under convenient conditions (0 °C, 20 s), and various classes of electrophiles can be used. With sensitive substrates, an in situ trapping metalation in which TMPLi is added to a mixture of the azobenzene and ZnCl2 or MgCl2·LiCl was very effective for achieving high yields.